Crack in my wine glass
It looks like you have a face inside the glass wall, the subsurf modifier does not handle this kind of non-manifold geometry very well.

Look closely, see the face within the wall.


To get rid of it just go into wireframe view and select the spare face and delete it with Del > faces.


Edit:

I looked at your .blend file and since in your particular case you are using a solidify modifier to get the glass thickness you can't directly select the offending faces and delete them.  Just go into edit mode and select all with A, then hit W > remove doubles.  This will merge the duplicate vertices along the crack.

Here is a comparison:


See how before I removed doubles, when I selected the edge loop at the location of the crack only have “tails” in one direction?  This means there are double verts at that location.